GoAnimate

According to its creators, GoAnimate is "a platform that allows people to express themselves through animation without having to learn to draw or install any software.“

The tools found on GoAnimate are apparently easy to use (I haven't tried it out yet). Basic animations (under 2 minutes with audio upload capability) are free. If you want more functionality (the ability to upload your own images to animate and the option to make longer downloadable animations) requires a paid "premium" account.